SSRG International Journal of Civil Engineering Volume 7 Issue 10, 1-8, October 2020 ISSN: 2348 – 8352 /doi:10.14445/23488352/IJCE-V7I10P101 © 2020 Seventh Sense Research Group®

This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

A study on the strengthening of buildings

designed based on 3rd edition of 2800 codes by

utilizing viscous dampers Himan Mohammad Eisa*1

Department of Civil Engineering, Pardis of Urmia

University, Urmia, Iran

Received Date: 9 September 2020

Revised Date: 11 October 2020

Accepted Date: 17 October 2020

Abstract - One of the methods that have been

considered in recent years for the reinforcement of structures is the use of energy-absorbing systems. A

variety of energy-absorbing systems have been

developed and introduced, including liquid, viscous

dampers. The main purpose of this study is to evaluate

the efficiency of viscous dampers in absorbing forces

caused by earthquakes and seismic improvement of

structures and the feasibility of increasing the floors of

an existing structure by using these dampers. Three

different models with fixed plans and three different

numbers of floors as five, nine, and thirteen have been

selected for this purpose. The possibility of increasing one floor to them by using viscous dampers has been

investigated. The results indicated that by adding a

floor to the existing buildings, the stress ratio in some

columns and the relative displacement exceeds the

allowable limit; however, viscous dampers can

significantly decrease the stresses and displacements

and can be used to expand the number of floors of an

existing building.

Keywords: viscous dampers, building development,

seismic improvement, energy-absorbing systems

I. INTRODUCTION Viscose dampers were first used in the 19th century

to counteract the effects of cannonballs on ships. Later,

the use of these devices in the aerospace industry for

launching missiles. Until the first half of the 20th

century, this technology was also used in car factories.

The introduction of viscose dampers into the

construction industry began with experiments at the

University of Buffalo and in the early 1990s[1]. Then

many scientists and researchers have researched in the

field of viscous dampers.

Damping is one of the significant and inherent

characteristics of the structure. There are various

methods to apply damping to the structures. For

example, Mousaviet used the Rayleigh method to

consider the damping in double-layer braced barrel

vaults[2]. Bhaskararao and Jangid[3] examined the

seismic response of adjacent buildings connected to

dampers. In this research, the structural response of two

adjacent buildings connected to different types of

dampers under different earthquake stimuli has been

studied. The results show that connecting adjacent

buildings with different main frequencies with passive

dampers can effectively reduce both buildings'

earthquake responses. Shrimali et al. [4] investigated

the performance of a variable friction damper (VF).

They Considered two connection modes of adjacent 20-

story and 10-story frames connected by a friction

damper. Their results showed that dampers significantly

affect the seismic response of two adjacent and

identical buildings and reduce the response.

Patel [5] investigated using viscous dampers to

control the seismic response generated on adjacent

buildings with similar dynamic properties. The results

showed that viscous dampers' use reduces the seismic

responses by selecting the appropriate damping

coefficient. Separation of the base to prevent the direct

transfer of seismic force from the foundation to the

structure is an important practical measure in improving

the seismic performance of structures. Alimohammadi

et al. [6]. Modeled and analyzed a 4-story steel frame

with bending joints in SAP2000 software. The analysis

was performed using a nonlinear time history method.

Lateral displacement of separator level, lateral

displacement of structure, and floors' acceleration in

isolated flexural steel frames with different adduction

damping ratios have been investigated. The results also

show that under the influence of earthquakes in the near

and far areas, the base level's displacement is reduced

by increasing the additional damping.

Geometrical features and charismatic material play a

Himan Mohammad Eisa / IJCE, 7(10), 1-8, 2020

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big role in the behavior of the structures. For example,

recent studies on STMF structures revealed how

changing the special region's geometric properties in an

STMF can change its behavior and response reduction

factor[7]. Farahbod and Gharshi[8]investigated the

Effect of viscose dampers on high-rise steel buildings'

seismic performance with a core system and arm

restraint. For this purpose, three buildings of 20, 30,

and 40 were modeled in three dimensions with an

asymmetrical plan and dimensions of 25 × 25 meters

and a floor height of 5.3 meters using the finite element

software. These models were subjected to nonlinear

time history analysis under three distant earthquake

records, regardless of wind load, once by changing the

bracing position in different stories and again by

changing the braking location equipped with viscous

dampers in different stories. Examination of these

parameters showed that in the case of using mortar

viscosity, the average maximum amount of roof

displacement is 27% in the 20-storey building, 33% in

the 30-storey building, 37% in the 40-storey building,

and 13% in the 20-storey building in the 30-storey

building. Percentage and in the 40-story building, 21%

decreased compared to the state without dampers.

II. Viscous dampers

Viscous dampers were first used in the late mid-19th

century to offset cannon hits on ships. In the first half of

the twentieth century, an automobile company

extensively increased their endurance and used them for

the needs of vehicle suspension systems. During the

Cold War, viscous dampers were used to separate silos

and rocket launchers, and their use and Development

for large cannons and warships increased. In the late

1980s, a small variety of these dampers were widely

used by military contractors for civilian purposes. A

military contractor named Taylor [8]conducted

experiments in collaboration with the National Center

for Earthquake Engineering at New York University in

Buffalo and investigated the adaptability of viscous

dampers in building applications to withstand wind and

earthquake motion. Since then, viscous dampers have

been used in more than 110 large structural

applications. Viscous dampers were used in dimensions

of 40 cm to 1.4 m. Their output power range is from

44.5 kN to 9 MN. A viscous damper consists of only a

few parts. The main part of it is a piston, which has a

reciprocating motion. The liquid

Fig 1. Viscous dampers

pass through the holes, and the velocity of the liquid

produces force. Figure 1 shows a viscous damper.

Damping can also be simulated, such as material

nonlinearity, in different ways. Materials can influence

the structures' behavior in various ways; for example,

Mousavi et al. and Ali Mohammadi et al.[9] [10]

investigated the behavior of the material in structural

systems from various viewpoints.

There are several important advantages to using

viscous dampers. The damping force produced by

viscous dampers in a structure is inherently non-phase,

with the structure's maximum response during a seismic

event. It is the highest of the lateral forces. The

damping force is the lowest. For this reason, viscous

dampers can reduce acceleration stori shear and base

shear. Viscous dampers could also be combined with

shape memory alloy (SMA) wires to take advantage of

these materials' energy-absorption and superplastic

properties [12]. Viscous dampers have become a sealed

device, making them less sensitive to the atmospheric

hazards that friction dampers must withstand. Taylor

[8]stated that the high quality of products using

inelastic seals and polished pistons with a 35-year

warranty eliminates the need for regular maintenance.

Finally, the viscous damper's performance is almost

heat-independent, and the same viscosity damping

equation is valid for all frequency levels, making it

easier to model more accurately than the more viscous

elastic damper. Due to the low compaction of viscous

fluid, starting to work is accompanied by a blow to the

viscous damper, and for this reason, viscous dampers

act in small structural deformations such as rigid

systems. According to Taylor [8], these dampers do not

produce any damping at displacements of less than 2

mm. Although in recent years, there is some

improvement in computational fluid dynamics and

standard combined methods for a subsonic flow field,

unfortunately, simulating the viscous dampers is still

complex to model[13], [14]. Because their output force

is based on their velocity, and the force on the rest of

the structure is based on deformation, relative damping

assumptions may be invalidated.

Himan Mohammad Eisa / IJCE, 7(10), 1-8, 2020

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III. The methodology of the research

In this study, the purpose is to investigate the

efficiency of viscous dampers in absorbing earthquake

forces and seismic improvement of structures and the

feasibility of increasing the floors of an existing

structure using these dampers. Accordingly, three

models with different numbers of building stories will

be studied. In this way, the feasibility of increasing the

floors using viscous dampers will be investigated. The

specifications of the three models under study are five

stories to the six-story building, nine stories to the ten-

story building, and thirteen-story to the fourteen-story

building for model numbers one, two, and three,

respectively. The steps of researching each of the

models are as follows:

1) Modeling, analysis, and design of an n-story

building by spectral method

2) Modeling, analysis, and design of a 1 + n floor

building by spectral method

3) Adding a floor to the designed n-floor building

and analyzing the time history, and examining changes

in displacements and stresses in the n + 1-floor

structure

4) Seismic improvement of 1 + n floor structure

using viscous dampers

5) Analysis and design of time history of 1 + n floor

building by increasing the damping of the structure and

determining the appropriate damping percentage

6) Spectral analysis and design of 1 + n floor

building with damping obtained from step 5

7) Compare the analysis results of items 1 to 6 by

presenting tables and graphs.

IV. Modeling specifications and input parameters

The general characteristics of the studied sample are

given in Table 1. Also, figure 2 shows the typical

architectural plan of the floors of the studied building

that was used in this research that was identical for

all the case studies structures.

Fig 2.Architectural plan of floors

The concrete material and steel material

specifications and design parameters used in this study

are described in Table 2In this research, ETABS

software has been used to model and design the sample

building and Excel software, to analyze the results of

structural analysis and to present the graphs. Table 3

shows the loads used in modeling.

In general, for the seismic design of buildings, the

base section obtained from the equivalent static method

must be calculated. For this purpose, according to the

building's characteristics and its structural system,

earthquake coefficients in the two main directions of

the building should be determined according to the

relevant design codes, which 2800 standard code used

in this study.

Table 1.General specifications of the project Location Structure

type

Building

type

Story

height

Soil

type

Lateral loading type gravity

bearing

system type

Floor

thickness

Urmia,

Iran

concrete residential 3.2

meter

No III Medium bending frame

in both directions

Beam block

roof

0.3 meter

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Table 2. The concrete material and steel material

specifications

Concrete material Steel material

Unit weight

(kg/m3)

2500 Unit weight

(kg/m3)

7850

Elastic modulus

(kg/cm2)

26518

0

Elastic modulus

(kg/cm2)

2 E6

Poisson’s ratio 0.15 Yield tension

(kg/cm2)

4000

Compressive strength of

concrete (Mpa)

25 Ultimate strength

(kg/cm2)

6000

Table 3. Summary of the loads on the floors

Location Dead load

(kg/m2)

Live load

(kg/m2)

Walls load

(kg/m2)

Roof 455 150 -

floors 402 200 100

Also, spectral dynamic analysis and time history

methods have been used to perform structural analysis

and design the models. It should be noted that the use of

dynamic methods firstly increases the accuracy of the

design and makes the distribution of forces in the

structure more rational. Secondly, in regular structures

or some irregular buildings, it can lead to being

designed to be lighter (due to the reduction in the

amount of base cut compared to static analysis. By

performing modal analysis, the specifications of

different modes of the structure are calculated by the

ETABS software. In the spectral analysis method, each

vibration mode of the structure is practically like an

independent structure. In the modal analysis method,

structural responses such as internal forces of members,

displacements, shear of the floors, and the reaction of

supports are obtained for each mode separately.

However, it should be noted that because the vibration

alternation times of different modes are different from

each other, the maximum structural responses for

different modes do not occur simultaneously.

Therefore, it is not possible to determine the response

of the whole structure. There are two main methods for

combining the effects of modes: the square root total

method (SRSS) and the complete square combination

method (CQC). Of the two methods, the CQC method

is more accurate and can be used in all structures.

V. Results of analysis

As mentioned in section 2, model number one is a

five-story building, and the possibility of increasing it

by one floor using viscous dampers was investigated in

this study. Model numbers two and three are a nine-

story building and a thirteen-story building. The

possibility of increasing it by one floor using viscous

dampers was investigated in this study. The calculation

method was the same for all these three models

mentioned in this section, as below.

After modeling and analyzing the five-story building

and determining and applying the correlation

coefficient according, the five-story building's design

was done, and the sections of beams and columns of the

structure were obtained. The structure was designed so

that the stress ratio in the beams and columns and the

relative displacement of the floors reached its allowable

value by making trial and error in the dimensions of the

beam and column sections. In addition to the stress ratio

in the structure members, the relative displacement of

these elements is also very important in making trial

and error to optimize the design schemes [15] further.

Because the lateral load-bearing system of the structure

is flexural in both directions, the relative displacements

often control the stresses. The dimensions of the

sections should be increased to allow them. To compare

the maximum amount of floor displacements in

different structures, the floors' displacements are

extracted from the results of software analysis.

After analyzing and designing the five-story building

in the previous stage, one floor was added to the

existing five-story building. The six-story structure was

analyzed dynamically by time history and under scaled

accelerometers. After performing the analysis, the

values of stress ratio in columns and structural

displacements were investigated. After modeling and

analyzing the six-story building in ETABS software

and determining and applying the correlation

coefficient according to the method, the six-story

building design was done. The sections of beams and

columns of the structure were obtained. To design a six-

story building, by making trial and error in the

dimensions of the sections of beams and columns and

controlling the amount of stress in the sections, the

optimal possible dimensions for the six-story concrete

structure was reached. To improve the 5 + 1-story

building's seismicity and allow relative stresses and

relative displacements, viscous dampers have been

used.

Meanwhile, in this stage, to perform analysis and

design, the method of dynamic analysis of time history

has been used. Then, the damping coefficient, stiffness

of the dampers, and the type of dampers are done.

Finally, the changes in the columns' stress ratio and the

number of displacements after adding a viscous damper

to the structure are examined.

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A. Calculation of damping coefficient and hardness

of dampers

The damping ratio created in the structure by the

damper can be calculated using Equation 1:

(1) 𝜁𝑑 =𝑇∑𝐶𝑗𝜑𝑟𝑗

2 𝑐𝑜𝑠2𝜃𝑗

4𝜋 ∑𝑚𝑖𝜑𝑖2

In the above relation T, the period of the main mode

of the structure, Cj, the attenuation coefficient of floor

j, φrj, the relative horizontal displacement of the two

ends of the damper due to deformation of the structure

in the first deformation mode, θj The displacement of

floor i is due to the deformation of the structure in the

first mode of displacement. In the following, each of these parameters is calculated, and finally, the

damping coefficient is calculated. Dampers are

located in the side openings of frames 1, 5, A, and F.

The location of the dampers can be seen in Figure 3.

Table 4, the damping coefficient of type 1 dampers, is

calculated using Equation 1 with a damping ratio of

15%.

The stiffness of the dampers is obtained from

Equation (2).

(2) τ =C

K𝑛𝑜𝑛𝑙𝑖𝑛𝑒𝑎𝑟

In this regard, C is the same damping coefficient

calculated in the previous section. The parameter τ is

equal to the ratio of the damping coefficient to the

stiffness of the damper. If the stiffness is set so that this

parameter is obtained between 0.01 to 0.001 inverse of

the structure's natural frequency, it will be appropriate.

Therefore, the value of parameter τ was considered to

be 0.01 inverse of the natural frequency of the structure.

The natural frequency of the structure can also be

calculated from Equation (3).

(3) 𝜔𝑛 =2𝜋

𝑇

(a) (b)

(c) (d)

Fig 3. Location of dampers in the 1 + 5-floor

building for a) frame 1, b) frame 5, c) frame A, d)

frame F

In this regard, T is the main periodicity of the

structure. Table 5 shows the hardness of dampers.

After obtaining the optimal damping of 15% in the

previous stage, in this stage, the 5 + 1-storey building

has been analyzed and designed by the spectral

method with damping of 6.2%. With increasing the

damping of the structure by 6.2% in the structure of

5+1 floors, it was observed that the stress in the

columns that exceeded the strength of the member

reached the amount of resistant stress.

Table 4. Calculation of damping coefficient of type 1 dampers with a damping ratio of 15% Story Modal Disp (𝜑𝑖) Modal Drift (𝜑𝑟𝑗) (kg) im cos𝜃𝑗 𝑚𝑖𝜑𝑖

2 𝜑𝑟𝑗2 𝑐𝑜𝑠2𝜃𝑗 C

𝑘𝑔−𝑠𝑒𝑐

𝑚

6 0.0039 0.0006 26336.432 0.477 0.4005771 8.19104E-08 2593523

5 0.0033 0.0008 26136.015 0.477 0.2846212 1.45619E-07

4 0.0025 0.0007 27814.154 0.477 0.1738385 1.11489E-07

3 0.0018 0.0008 29805.101 0.477 0.0965685 1.45619E-07

2 0.001 0.0006 30133.991 0.477 0.030134 8.19104E-08

1 0.0004 0.0004 31469.846 0.477 0.0050352 3.64046E-08

sum - - - - 0.9907745 6.02952E-07

Himan Mohammad Eisa / IJCE, 7(10), 1-8, 2020

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This trend repeated for all three models. In analytical

models, the Rayleigh method is utilized to define

damping matrix. This method is one of the common

methods of defining the damping matrix in structural

engineering; for example, Mousaviet. al. and

Alimohammadi et al. [2], [6]used this method for defining the damping matrix in double-layer braced

barrel vaults in assessing the progressive collapse

probability in theses space frame systems.

B. Model one Figure 4-a shows the relative displacements of the

stories in the x-direction in different cases of model

number one. In the chronological analysis, only the

results of the most critical earthquake acceleration are

given. Figure 4-b shows the diagram of the relative

displacements of the stories in the y-direction in

different cases.

Figure 5-a shows the diagram of the maximum

displacement of the floors in the x-direction. Figure 5-b

shows the maximum displacement of the floors in the

y-direction in different cases of model number one.

According to these diagrams, it can be seen that the

displacements in the 5 + 1-floor building with dampers

are less than in other cases, which indicates the very

favorable Effect of these dampers on the behavior of

the structure.

C. Model two

Model number two studied in this research is a nine-

story building and the possibility of adding one story to

it using viscous dampers. Figure 6-a shows a diagram

of the relative displacements of the classes in the x-

direction. Figure 6-b shows the relative displacements

of the classes in the y-direction in different cases of

model number two.

D. Model three

Model number three studied in this research is a

thirteen-story building and the possibility of adding one

story to it using viscous dampers. Figure 7-a shows a

diagram of the relative displacements of classes in the

x-direction, and figure 7-b shows the relative

(a)

(b)

Fig 4. a) Diagram of the relative displacement of the

floors in the x-direction, b) the relative

displacements of the stories in the y-direction in

different cases in different cases in model number 1

Table 5. Calculatedstiffness of dampers K (kg/m) C

𝒌𝒈−𝒔𝒆𝒄

𝒎 𝛕 𝝎𝒏 T(s) Type

1365012105 2593523 0.0019 5.261 1.1943 1

1038003158 1972206 0.0019 5.261 1.1943 2

898294211 1706759 0.0019 5.261 1.1943 3

1262437368 2398631 0.0019 5.261 1.1943 4

1442571579 2740886 0.0019 5.261 1.1943 5

Himan Mohammad Eisa / IJCE, 7(10), 1-8, 2020

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(a)

(b)

Fig 5. a) Diagram of relative displacement of stories

in the x-direction, b) in the y-direction

Figu 6. a) Diagram of the maximum displacement of

floors in the x-direction,

Figure 6. b) Diagram of the maximum displacement

of floors in the y-direction

(a)

(b)

Figure 7. a) Diagram of relative displacement of

stories in the x-direction, b) in the y-direction

displacements of the classes in the y-direction in

Himan Mohammad Eisa / IJCE, 7(10), 1-8, 2020

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different cases of model three. In the chronological

analysis, only the results of the most critical earthquake

acceleration are given.

According to these diagrams, it can be seen that the

displacements in the 13 + 1 story building with dampers

are less than other cases, which indicates the very

favorable Effect of these dampers on the behavior of

the structure.

VI. Conclusions

In this study, the feasibility of developing the number

of floors of a building with a concrete structure was

investigated. Thus, three models with a different

number of floors were designed. After adding one floor

to them, the number of relative displacements and the

ratio of stresses in the structure members were

corrected using viscous dampers. After conducting

these studies and analyzing the different responses of

the structure and according to the results given in the

fourth chapter of the dissertation, summarize these

results could be mentioned as below.

1. Adding a floor to the existing building caused the

stress in some columns to exceed the resistant stress

and caused the relative displacement of the floors to

exceed the allowable value.

2. The addition of dampers to the developed building

caused the columns' stress to be less than the amount of

resistive stress in the member.

3. The addition of dampers to the developed building

caused the floors' relative displacement to be less than

the allowable value.

4. After examining the number of stresses and

relative displacements of floors in the three models in

the conditions of increasing the structure's damping, it

was shown that in 6, 10, and 14 story buildings with

increasing the damping by 6.2, 21 and 23, respectively.

Percentage, stresses, and relative displacements reached

their allowable values.

5. The results showed that in different modes of the

models, different earthquakes became more critical.

Still, among the earthquakes applied to the structure,

the El Centro earthquake, in most cases, creates more

critical conditions.

VII. Conflict of interest

The corresponding author states that there is no

conflict of interest.

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